In Greeek grammar, we use the word case to mean “how a noun is used in a sentence.” Here's a rough correspondence:

English Grammar
Greek Grammar
Greek name
SubjectNominative case
PossessiveGenitive case
ObjectAccusative case

There is a fourth case, the “vocative”, but it is not used often, and we will safely ignore it in this introduction.

Although Greek uses a consistent word order in its sentences, with subject first and object last, that’s not the main determiner of how a word is used (its case). Instead, Greek words change their endings to tell us how they are used. Ready for a big surprise?

We do this in English, too.

It only happens with pronouns, and you probably never even notice it until someone points out how they change their form when their usage changes:

She went to the store.
The clerk greeted her and handed over a small package.
The new camera was hers at last!

Up until now, we’ve been able to get away with just the nominative case, since the verb “to be” isn’t an action verb. But now that we have verbs that act on some object, we’re going to need accusative case, and we’ll eventually need genitive to denote who owns what. So, when we add case to the mix, we now have to think about three things when we use nouns:

 << How Nouns are Used Grammar Index Number, Gender, and Case >>